Production of metallic carbonyls



Patented Oct. 2, 1934 PRODUCTION METALLIC CARBONYLS Owen G. Bennett, Baltimore, Md, assignor to Catalyst Research Corporation,

Baltimore,

Md., a corporation of Maryland No Drawing. Application December 1, 1932, Serial No. 645,234

I 6 Claims. (01. 2s 203 This invention relates to the production of metallic carbonyls, especially those of iron, cobalt, and nickel. I

Many metals are capable of reacting with carbon monoxide to form carbonyls, but the attainment of satisfactory reaction and yields appears to be dependent upon the use of metal in a suinciently highly reactive state and substantially free from oxide. Apart from these two essential conditions the operating conditions, i. e. temperature and gas pressure, vary somewhat according to the particular metal and they are not as crucial or as fixed as the two requirements just mentioned. 1 v

Various modes of preparing metals for this reaction have been proposed and used, but all of those conceived heretofore and known to me have been subject to serious disadvantages. The reactivity of the metal, other things being equal, is dependent upon the particle size; i. e. the greater the degree of subdivision the higherthe activity owing, presumably, to the increase in exposed surface. To this end the common practice in preparing metals for carbonyl formation has been'to reduce a compound thereof, such as the oxide, carbonate,oxalate or other organic salt, withhydrogen at an elevated temperature. For instance, for this purpose iron oxide is reduced in hydrogen at' a temperature of about 500? 0., and I theoptimum temperature for reduction of nickel oxide lies between about 300 to 400 C.

Such procedures are disadvantageous, because the degree of heat necessary to effect'the reduction may be, and usually is, detrimental to attainment of maximum activity, because it causes appreciable sintering of the finely divided particles of metal. The activity of the metal is thereby reduced substantially. Moreover, by such procedures it has been difficult to prepare metal wholly free from oxide, because the last traces of oxide may not be reduced. Therefore the maximum activity toward carbon monoxide has not been obtained by. such procedures. Other procedures of preparing metals forthis purpose'are subject to these and other disadvantages, being, for example, tedious and impracticable commer cially.

It is among the-objects of this invention to provide a method offorming metallic carbonyls, in which the'metal is prepared in a state of exceptionally high activityand freedom from oxide by a simple, easy, efficient and inexpensive procedure, which overcomes, or minimizes, disadvantages heretofore'met with in this art, and

which provides suitable yields under more favorable operating conditions than heretofore.

The invention is predicated upon my discovery that carbonyl formation is favored by converting the carbonyl-forming metal into an amalgam, 6Q

removing mercury therefrom by vacuum distillation at relatively low temperature, and treating the metal thus prepared with carbon monoxide, the metal being protected during these steps against oxidizing influences. tages attend the preparation of carbonyls by this method. More particularly, the treatment of metalby this amalgamation procedure converts it to a state of exquisitely fine sub-division presenting unusually high activity, provides highly reactive metal free from contaminating oxides, and the distillation temperatures are, in general, lower than are required in oxide reduction procedures and do not detrimentally sinter the product. The great activity of the metal used in the practice of this invention is evidenced by its reactivity at low temperatures and gas pressures, and by the fact that it can be wholly converted to carbonyl.

In the practice of the invention an amalgam of the metal whose carbonyl is to be produced is first formed by any suitable procedure, of which several are known to those skilled in the art. For instance, massive metal may be treated with mercury, or the amalgam may be made by electrodeposition' of the metal at a mercury surface, e. g. at a mercury cathode. Preferably arelatively concentrated amalgam is formed, for reasons of economy. The pure amalgam is protected from oxidizing influences, as by main- Amalgams are generally more reactive than their individual constituents, for instance with respect to oxidizing influences. It is for this reason that the amalgams are protected by a non-oxidizing atmosphere in the practice of the invention. removal of mercury is unnecessary for its presence does not detract from the activity of the metal. Thus where desirable for any reason the mercury need not be completely distilled off,

although the major portion should be, so as to 110 Particular advan- 65 For most purposes a temperature 95 But for the same reason complete leave the porous material, which thus presents a larger reacting surface.

The distillation just described leaves the metal in a form presenting an enormously large surface, and free from oxide, so that the metal is extremely reactive. The highly reactive metal prepared in this manner is retained in a nonoxidizing atmosphere until it is ready for use, when it is contacted with carbon monoxide under appropriate temperature and pressure conditions. The volatile carbonyl iscQndensed from the efliuent gas stream by appropriately refrigerating it, as will be understood. These conditions vary according to the particular metal, and according to desired commercial practice. found that, in general, metal prepared as just described is reactive at much lower temperatures than can be satisfactorily used with metal prepared by procedures heretofore available, and that the extremely high gas pressures that have been necessary may be dispensed with.

The invention is particularly applicable to the preparation of carbonyls of iron, nickel and cobalt. The preparation of iron carbonyls has always been diiiicult, much more so than nickel carbonyl, for example, and has required higher temperatures, and pressures. For this reason the invention may be described more particularly with reference to iron carbonyl. As a non limiting example of the practice of the invention, iron amalgam is prepared by electrodepositing iron in mercury from a solution of an iron salt. To this end a solution of 350 grams per liter of ferrous ammonium sulfate may be electrolyzed using a mercury cathode. The solution is preferably slightly acidified with sulfuric acid, e. g. by the addition of about 0.25 gram of sulfuric acid per liter. The mercury should be kept agitated, and the electrolysis is continued until a relatively thick amalgam is formed. The current conditions are not critical, the only desideratum being that iron be deposited in a pure form.

The amalgam is washed free from residual solution without exposure to oxidizinginfluences, because amalgamated iron oxidizes rapidly and easily. The amalgam is then transferred to any suitable apparatus adapted for vacuum distillation, and the mercury is distilled 01f, e. g. at a temperature of about 350 C. The iron remains as a hard mass which is, however, exceedingly porous and presents an exceedingly large and highly reactive surface. It should be protected from oxidizing gases. When treated with carbon monoxide it reacts readily and completely to form iron penta-carbonyl, Fe(CO) 5.

The original Mend and Langer process of making iron carbonyl was very tedious and gave a yield of only about 1 percent, calculated upon the iron used. The most recent modification of that process, for the purpose of improving yields, requires an operating temperature of about 500 C. and gas at a pressure of about 200 atmospheres. In contrast with this, iron prepared in accordance with this invention is highly reactive to carbon monoxide at relatively low temperatures, for example 60 0., and is completely consumed upon exposure to sufficient carbon monoxide gas at ordinary atmospheric pressure.

As indicating the reactivity of the material prepared in accordance with this invention, 2-5 grams of iron prepared by the amalgamation method was treated with CO gas at 60 0., and 3 cc. of carbonyl was condensed in six hours. Although this yield appears to be slight, it is evidence of the highly reactive character of the I have iron because iron reduced from the oxide (as customary in this art) form only a faint trace of carbonyl under these conditions. Of course, the rate of reaction, and therefore the yield, may be increased by increasing the temperature and gas pressure in accordance with the practice customary in the art.

As further indicating the benefits to be derived from the invention, reference is made to the production of nickel carbonyl. According to the best prior practice nickel prepared by reduction must be heated to a temperature of about 100 C., or higher, and relatively high pressures are necessary, in order to obtain attractive yields. Such a procedure may yield only 1 cc. of nickel carbonyl per 10 cc. of metallic nickel per day.

Using nickel prepared in accordance with this invention, and passing carbon monoxide over it at atmospheric pressure and room temperature (25 C.) yields of 7 cc. of nickel carbonyl per hour were obtained. It appears that the reaction is sufficiently rapid that, for a given volume of gas, the yield of carbonyl is independent of the rate of flow of the gas, provided proper condensation of the carbonyl is achieved.

In all instances of the practice of the invention the metal is completely converted to carbonyl, proving that the whole of the metal is in a sufliciently active state to completely react under these conditions. Suchcomplete conversion is unusual with the less reactivemetals, such as The invention thus provides a process of making metallic carbonyls, and particularly those of iron, nickel and cobalt, which provides and uses metal in a more highly reactive state than has been available heretofore, which simplifies the operating conditions, provides for suitable yields at lower temperatures and gas pressures than have been necessary heretofore, and which effects other economies due to the fact that the metal is sufficiently reactive to be completely converted into carbonyl.

According to the provisions of the patent statutes, I have explained the principle of my invention and have described what I now consider to represent its best embodiment. However, I- desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically de- 125 scribed.

I claim:

1. In a method of making metallic carbonyls, the steps comprising forming an amalgam of a carbonyl-forming metal, subjecting the amalgam 3 to vacuum distillation to remove mercury therefrom, contacting the metallic residue with a stream of gaseous carbon monoxide, condensing metallic carbonyl from the gas stream after con-- tact with the metal, and during said steps main- 135 taining said amalgam and metal under nonoxidizing conditions. I

2. In a method of making metallic carbonyls, the steps comprising forming an amalgam of a carbonyl-forming metal, subjecting the amalgam 4 to vacuum distillation to remove mercury therefrom, contacting the metallic residue with a stream of gaseous carbon monoxide at a temperature and pressure adapted to enhance carbonyl formation, condensing metallic carbonyl from the 145 gas stream after contact with the metal, and during said steps maintaining said amalgam and metal under non-oxidizing conditions.

3. In a method of making metallic carbonyls, the steps comprising forming an. amalgam of a 150 the steps comprising forming an amalgam of said metal, subjecting said amalgam to vacuum distillation and removing mercury therefrom, contacting the metallic distillation residue with a stream of gaseous carbon monoxide, condensing metallic carbonyl from the gas stream after contact with the metal, and during said steps maintaining said amalgam and metallic distillation residue under non-oxidizing conditions.

5. In a method of making a carbonyl of a metal of the group consisting of iron, cobalt and nickel, the steps comprising forming an amalgam Of said metal, subjecting said amalgam to vacuum distillation and removing at least the major part of the mercury therefrom, contacting the metallic distillation residue with a stream of gaseous carbon monoxide at a temperature and a pressure adapted to enhance carbonyl formation, condensing metallic carbonyl from the gas stream after contact with the metal, and during said steps maintaining said amalgam and distillation resi due under non-oxidizing conditions.

6. In a method of making a metallic carbonyl, the steps comprising forming an amalgam of the metal by electro-deposition at a mercury surface, subjecting the amalgam to vacuum distillation and removing at least the major part of the mercury therefrom, contacting the metallic distillation residue containing a minor proportion of mercury with a stream of gaseous carbon monoxide at a, temperature and a pressure adapted to enhance carbonyl formation, condensing metallic carbonyl from the gas stream after contact with the metal, and during said steps maintaining said amalgam and distillation residue under non-oxidizing conditions.

OWEN G. BENNETT. 

